1. Field of Invention
The present invention relates to a method for forming a gate structure, and more particularly to a method for forming a T-shaped gate structure.
2. Description of Related Art
A GaAs device tends to have less noise than a silicon device, especially at a high frequency resulting in higher carrier mobilities and lower resistive device parasitics. These properties recommend applying a GaAs circuitry in a mobile phone, satellite communication, a microwave point-to-point link and a higher frequency radar system.
To reduce a gate length without increasing a gate resistance, a T-shaped gate structure is commonly used. The T-shaped gate is composed of an upper wide layer which increases a cross sectional area of the gate for reducing the gate resistance, and a small footprint with a reduced gate capacitance. In general, the T-shaped gate is fabricated using e-beam lithography. It is a reliable technology because the resolution of e-beam lithography can be very high. However, it also has a very low throughput which limits its applications on mass production.
Therefore, a new T-shaped gate manufacturing method is needed.